Focal P20F 8-inch Subwoofer
When referencing French speaker virtuoso Focal there’re two main observations most will make. The first of course is sound, with all and sundry readily advocating Focal’s terrific sounding drivers. While this aspect may be a given, many punters also remain hitherto unawares of the materials-related genius of this company, not only concerning metallurgic related elements but its stunning prowess covering most other materials in general.
Since its actual inception in 1979 Focal has mastered an astounding array of materials, ranging from ‘fiddly’ to ‘downright problematic’, with some of the latter being so difficult that even military companies refused to work with them. This territory, that most manufactures resign to the ‘too hard’ basket, is the exact territory Focal revels in; with the new Flax series subwoofers demonstrating this unique ability most succinctly.
Pertaining to subwoofers, there are a few basic principles that’ll forever remain unchanged. At a most basic level, they’re simple devices that move air around, with the diaphragm’s forward motion creating high pressure compression waves and backward motion creating low pressure rarefaction waves. This diaphragm (cone) is the critical part of the design, as it’s the primary piece that causes the air molecules to dance in motion.
For this reason Focal focuses much of its research and development on cone material development, as the resulting sound will be directly impacted by the intrinsic qualities of the materials used. Not only must weight and mass be kept to an absolute minimum to allow lightning quick reactions, it must also possess serious strength, as that cone is acting as a piston which means any movement-related structural flaws will quickly be exposed.
Then just to make life interesting you throw in a curve ball in the form of something called damping; the cone must be well damped so the subwoofer doesn’t excessively colour the sound. This is where nature rears its ugly head because there is no material that’ll homogenously satisfy all of these criteria completely. In response to this conundrum Focal developed a ‘W’ sandwich cone design, which sees multiple layers employed, each of which excel in a specific quality and together equate to a most effective solution to the aforementioned problem.
The central layer of this ‘W’ sandwich is the one responsible for the mechanical damping and for many years Focal has enjoyed enviable success utilising non-woven fibres of carbon in numerous ranges of speakers. However, while the abilities of these carbon ‘W’ sandwich cones remain exceptional, they are growing a little long in the tooth. So back to the drawing board went Focal, starting out by laying down a few prerequisites for the new material.
First up, it had to retain a low mass and density. Secondly it had to possess a high tensile (Young’s) modulus and of course it also needed to enjoy superb internal damping characteristics. The desire for superior tensile modulus is nothing new. Young’s modulus represents the point at which a mechanical load would cause elongation to the entire length of the cone, and while in reality physical deformation would occur long before this point is reached, it’s still paramount that any material have a high Young’s modulus thus making it more resilient to bending and physical distortion under duress. Internal damping is also of critical importance, and is characterised by a coefficient known as dissipation factor. Basically put, at the diaphragm’s breakup frequency, the higher the dissipation factor means the less severe the resonance as surplus energy is distributed within the material, ergo equating to lower colouration and superior tonality.
Rummaging through various materials with gusto reminiscent of a Monty Python skit, Focal engineers happened upon flax, a material possessing innately neutral properties in addition to superior strength. Also handy was the fact that France is one of the main cultivators of flax in Europe, with a certain region’s countryside being covered in it. One could also state it’s been sitting right under their nose for more than just a little while, as flax is one of the oldest textiles known to man, with roots tracing back to 4th century BC Egypt.
What’s rewarding, however, is observing just how Focal’s engineers weave (no pun intended) their magic in bringing the flax material to life. Taking the aforesaid ‘W’ sandwich fibre cone, Focal omitted the central carbon weave and instead inserted a meticulously-designed flax layer between the 0.04mm acrylic plexiglass layers. The reason for this is that flax is comprised of around 70 percent cellulose with each fibre being a single elongated cell measuring between 60 and 100mm in length and boasting a width somewhere between seven and 40 micrometres.
Due to these inherent characteristics flax is superior to previous composite materials in that it offers similar strength but retains superior damping abilities. As an addendum I should also make mention of its weight. Because flax is a hollow core material it’s around half the weight of materials such as fiberglass, making it ideal for cone construction. It’s also non-woven meaning its thickness can easily be altered along the radius of the cone without mass becoming an overbearing concern.
Small sub – big sound
With the materialistic jargon out of the way let’s now turn our attention to the subwoofers themselves. There are three in the range being 8-, 10- and 12-inch and, despite many hazarding the supposition that we’d reach for the largest, we instead chose to review the smaller P20F.
Starting with the cone; it’s a specially-profiled 200mm diaphragm constructed from the abovementioned flax material and lining the top edge is a carefully shaped butyl rubber surround. Working with this and holding everything concentric is a flat rolled poly-cotton spider, joining the cone where it meets the voice coil top retainer cap. These work in harmony providing excellent resistance against radial and axial float, while also allowing the entire assembly to linearly move fluidly and with an efficiency of 82.5dB.
Attached to the bottom of the spider is the large 38mm fiberglass former which holds the tightly wound copper 4-ohms voice coil precisely within the densest magnetic fluxes allowing for an Xmax of 10mm. Encircling the motor and providing the magnetic force is a double-stacked 120mm x 32mm ferrite magnet and the entire 117mm deep affair is held rigidly in place thanks to a very open, aerodynamically transparent stamped steel frame which has been powder coated in the traditional Focal grey and adorned with emblems on the web fingers.
The cooling air follows an interesting trajectory courtesy of specially designed perimeter intake ports which are situated on the actual back plate. These take in cool air and move it along the outside of the voice coil gap before marrying it up with the cool air flowing through the spider. From here, it travels down through the pole and out the 10mm bell-mouthed central exhaust port, also located on the back plate. This gives the motor a power handling ability of 250 watts continuous and because the steel back plate is extended it can handle peak bursts of over double that.
When talking 8-inch subwoofers and their associated enclosures, many harbour the illusion that smaller subs only play higher frequencies something which is untrue. Assuming you’re not using a slim subwoofer with a low Xmax, and that you’ve designed your enclosure with the right Qtc for both your tastes and your car shape, you’ll get a wonderfully deep roll off. This should not be confused with sound pressure level, for this is something that a single 8-inch will struggle a little with.
However, if you’re restricted depth-wise to an 8-inch subwoofer and want copious levels of bass, use multiple drivers. Utilising Pi x R2 you’ll find an 8-inch is 50.26si. That means two are almost equivalent to a 12-inch (113.09si) and three are just shy of a 15-inch (176.71si). Not being a bass head I opted to stick with my single 8-inch and settled on a sealed 20.28l enclosure which returned me a Qtc of 0.707.
I entered the auditioning process with a certain degree of trepidation, as 8-inch subwoofers often struggle as they try a little too hard to impress. Mainly in terms of control, because their suspension is either designed to extend as much as possible or, on the flipside concerning sound pressure, wherein the suspension is so tight in order to attain incredible control that they cannot move fluidly. Thankfully, Focal has nailed these issues via its use of flax technology.
Not only does the P20F output a clean sound, it offers plenty of volume when pushed too. Commenting first on the quality of the musical reproduction; the suspension system works harmoniously to present you controlled subsonic energy you can actually listen to as opposed to it just smacking you in the skull. From gentler genres like classical and jazz, with their lingering lower bass notes, through to the faster genres of metal and dance with its lightning fast demands, the P20F handles them all without ado.
When it comes to pushing the subwoofer for serious volumes I’ll be the first to admit it’ll start to struggle beyond the 120dB/60Hz point; however, that said, the strength of the cone is still evident as the sound remains extremely controlled right up to the point of complete physical failure.
In what can only be described as a somewhat familiar occurrence, Focal has again created a superior design to its predecessors in every way. The flax subwoofers weigh less, cost less, look better, are stronger and, put simply, will outdo many competing subwoofers thrice the price.
While continuous improvement has always been Focal’s way, it does make it rather tedious if you’re the poor competition.
FOR: High levels of engineering; Truly unique & new diaphragm material; Sounds terrific
AGAINST: Reaches its limit under high SPL demands
Type: 8-inch single voice coil subwoofer
Power Handling: 250 watts continuous, 500 watts maximum
Frequency Response: 39Hz – 800Hz